The work will proceed in the following directions: 1. Exploration of the function of the (2Fe-2S) cluster in aconitase and the various states the enzyme has been found in with respect to the behavior of its Fe-S cluster and SH-groups. Mossbauer studies on the enzyme will be attempted. 2. Further studies of early intermediates in the reaction of cytochrome c oxidase with O2, with particular attention being given to a form with a novel EPR signal (J. Biol. Chem., 253, 6637-6640 (1978)). 3. Further development of rapid mixing and freezing techniques suitable for subzero work with attempts to include an optical rapid-scanning system for the liquid state prior to freezing.